1. Field of the Invention
The present invention relates to a high-density optical disc such as a high density-digital versatile disc (HD-DVD) or Blu-ray disc, which includes a lead-in area, data area and lead-out area.
2. Description of the Related Art
FIG. 1 is a view illustrating the structure of a conventional digital versatile disc (DVD). The DVD 10 has a thickness of 1.2 mm and a diameter of 120 mm. The DVD 10 includes a center hole having a diameter of 15 mm, and a clamping area having a diameter of 44 mm so that a turntable and damper provided in an optical disc device can clamp the DVD 10.
A data recording layer based on a pit pattern is formed on the DVD 10. There is a distance of approximately 0.6 mm between the data recording layer and the surface of an optical transmission layer, which is arranged between the data recording layer and an objective lens (OL) of an optical pick-up provided in the optical disc device. The OL of the optical pick-up for the DVD has a numerical aperture (NA) value of 0.6.
As shown in FIG. 2, a high-density optical disc 20 such as a high density-digital versatile disc (HD-DVD) or Blu-ray disc has a thickness of 1.2 mm and a diameter of 120 mm. The high-density optical disc 20 includes a center hole having a diameter of 15 mm, and a clamping area having a diameter of 44 mm so that a turntable and damper provided in an optical disc device can clamp the high-density optical disc 20. There is a distance of approximately 0.1 mm between a data recording layer and the surface of an optical transmission layer, which is arranged between the data recording layer and an objective lens (OL) of an optical pick-up provided in the optical disc device.
The OL of the optical pick-up for the high-density optical disc has a relatively larger NA value of 0.85, in comparison with the OL of the optical pick-up for the general DVD. In order for high-density recording data to be reproduced or recorded, the high-density optical disc uses a laser beam having a relatively shorter wavelength in comparison with the general DVD. That is, a laser beam having a wavelength of 650 nm is used for the general DVD 10, while a laser beam having a wavelength of 405 nm is used for the high-density optical disc so that the high-density recording data can be reproduced or recorded.
Thus, in a state where the OL of the optical pick-up for the high-density optical disc is closer to the recording layer of the high-density optical disc, the optical disc device employs a laser beam having a relatively shorter wavelength, and enables an NA value for the OL to be increased, thereby forming a small beam spot of the laser beam, having an increased light intensity, on the high-density recording layer. Further, an optical transmission layer transmitting a laser beam having a short wavelength can be reduced. Hence, variations of the laser beam's properties and aberration occurrence can be minimized.
As shown in FIG. 3, the high-density disc includes a lead-in area 201, data area 202 and lead-out area 203. In the lead-in area, are recorded control information needed for recording or reproducing data of the high-density optical disc, e.g., information associated with a size of the disc, a disc structure, a data recording density, a data area allocation, etc.
Therefore, when the high-density optical disc 20 is inserted and loaded within the optical disc device, the control information recorded in the lead-in area 201 is first read and confirmed. The optical disc device refers to the control information and then performs a sequence of reproduction or recording operations for reproducing data recorded in the data area 202 or recording data in the data area 202.
In the lead-in area 201, data area 202 and lead-out area 203, a channel bit length and data bit length are 80.00 nm and 120 nm in the case of a 23.3 GB high-density optical disc, respectively. In the case of a 25 GB high-density optical disc, the channel bit length and data bit length are 74.5 nm and 111.75 nm, respectively. In the case of a 27 GB high-density optical disc, the channel bit length and data bit length are 69.00 nm and 103.50 nm, respectively. Minimum mark/space lengths of data recorded in the areas 201, 202 and 203 are the same as each other.
As described above, the optical disc device must first and correctly read and confirm the control information recorded in the lead-in area so that the data of the high-density optical disc is reproduced or recorded. At this time, the interference between a mark and space may occur in high-density recording data. Further, scratches or dust on the surface of the optical disc can adversely affect the recording and reproduction of high-density recording data. For this reason, there are problems in that the control information cannot be appropriately read and hence a data reproduction or recording operation cannot be appropriately performed.